1. Field of the Invention
The present invention relates to a process for producing prussic acid. More particularly, the present invention relates to a process for producing prussic acid by subjecting methanol to ammoxidation in a gas-phase contact reaction.
2. Description of the Related Art
Prussic acid is produced by decomposition of formamide, reaction of methane with ammonia, ammoxidation of methane, etc. A large portion of the prussic acid consumed is a by-product formed when propylene is subjected to ammoxidation to produce acrylonitrile.
Prussic acid has been increasingly used as raw material for acetone cyanohydrin, adiponitrile, chelating agent such as EDTA and the like, and also used for gold recovery. The gap between its supply and demand has been becoming more obvious.
In view of the above situation, the present invention have been completed in order to develop a novel process for producing prussic acid by ammoxidation of methanol, which has excellent industrial applicability.
For production of prussic acid by ammoxidation of methanol, various catalysts are known such as molybdenum oxide, described in U.R.S.S. Patent No. 106226; an oxide containing molybdenum, bismuth and other elements, described in U.S. Pat. No. 3,911,089; an oxide containing antimony and at least one element selected from the group consisting of iron, cobalt, nickel, manganese, zinc and uranium, described in JP-A-51-10200; an oxide catalyst containing manganese and phosphorus, described in U.S. Pat. No. 4,457,905; an antimony phosphate, described in U.S. Pat. No. 4,511,548; and so forth.
In order to improve the iron and antimony-based oxide catalyst described in JP-A-51-10200, the present inventors proposed an oxide catalyst containing iron, copper and antimony, in U.S. Pat. No. 4,461,752; an oxide catalyst containing iron, copper, antimony and phosphorus, in U.S. Pat. No. 5,158,787; and a catalyst containing iron, antimony and phosphorus as essential components and iron antimonate as a crystal phase, in U.S. Pat. No. 5,094,990. The present inventors further proposed improved processes for catalyst production, in U.S. Pat. No. 4,946,819, U.S. Pat. No. 4,981,830, etc. Theses processes showed progresses in various respects, but still had points to be improved for industrial application.
That is, in producing prussic acid by ammoxidation of methanol, the above-mentioned catalysts require a high oxygen-to-methanol ratio in a mixed raw material gas in order to avoid a reduction in prussic acid yield or a reduction in catalytic activity with time. Consequently, when prussic acid is produced industrially with the catalysts, the reaction must be conducted at a low methanol concentration, which results in a lower productivity.
The present invention has been completed in order to (1) alleviate the above-mentioned problems of the prior art and (2) provide an economical process for producing prussic acid, which uses a catalyst having significantly improved redox stability, which enables an efficient reaction at a low oxygen-to-methanol ratio of mixed raw material gas, and which gives prussic acid as intended product at a high yield, at a high selectivity and stably with the lapse of reaction time.